Various efforts have been directed toward replacing machined metal parts with lighter weight molded materials. For example, in the aircraft industry, some metal parts have been replaced by plastic or composite parts that are formed using any of a variety of techniques. In addition to weight savings, parts made of polymeric materials may be manufactured more economically, due in part to the reduction of machining time and material waste.
Prior efforts to manufacture relatively high strength parts using polymeric materials have involved compression molding sheet-molding compounds, and laying up various forms of composite laminates using thermoset materials. Each of these prior efforts may have disadvantages. For example, low viscosity thermoset materials have limited flow distances during molding, and therefore may not be capable of producing parts of higher complexities. The use of sheet forms may not be suitable for making parts that are small, complex or have changes in cross sectional geometries. Existing manufacturing techniques may also require relatively complex layups and/or complicated molds which may not be cost effective for some applications. Finally, polymeric parts made by existing processes may not exhibit mechanical properties that are substantially the same in all directions. For example, laminated parts may not possess the same mechanical strength in both the in-plane and through-the-thickness directions of the laminate. Similarly, molded thermoset-resin chopped fiber parts may suffer from low mechanical strength in the through-the-thickness direction.
Accordingly, there is a need for a method of high flow compression molding high strength, complex polymeric parts that exhibit essentially isotropic or quasi-isotropic mechanical properties. There is also a need to replace machined metal parts with composite materials in order to reduce both part weight and manufacturing costs.